Marine instrument

ABSTRACT

A marine speed sensor mounted in a housing which may also include a temperature sensor and a sonic transducer. The speed sensor includes a paddlewheel for producing an electromagnetic field. The paddlewheel is rotatably mounted adjacent the housing and exposed at top and bottom and mounted between support members extending from the housing.

This application is a continuation of application Ser. No. 616,289,filed June 1, 1984, now U.S. Pat. No. 4,555,938.

TECHNICAL FIELD

This invention is in the field of marine instrumentation for providinginformation with respect to the speed of a marine vehicle through water,and the depth and temperature of the water.

BACKGROUND ART

Instruments for measuring and displaying speed or velocity of a marinevessel through water have utilized a wide variety of sensors (See, forexample, U.S. Pat. No. 4,206,637--paddlewheel interrupts photodetector;U.S. Pat. Nos. 3,531,988; 3,496,770; 3,457,782--paddlewheel with magneton each paddle or paddle made of magnetic field permeable material whichis sensed by electromagnetic pick-up coil; and U.S. Pat. No.3,706,224--paddlewheel with magnet on each paddle which interruptscurrent flow in a circuit).

Similarly, numerous instruments exist for providing sonic signals fordepth sounding or fish locating. (See, for example, U.S. Pat. No.4,110,727 and various references cited therein.)

It has also been found helpful for marine navigation and fish finding tomeasure water temperature by various means.

A need exists, however, for a low cost, instrument which will provideinformation with respect to all three parameters of speed, temperatureand distance in a convenient integrated assembly for ease in mounting.

For the most part, prior art speedometers are mounted through the hullof the vessel requiring the drilling of a large hole in the hull and theattendant sealing problems (See the knotmeter of U.S. Pat. No.3,531,988). Additionally, with the exception of the transom mountedspeedometer, it is customary to completely enclose the paddlewheel speedsensor except for a small portion in which the paddle extends into thewater (See U.S. Pat. No. 3,457,782, for example). In such "closedcavity" devices, the speed sensor becomes non-linear at higher speedsof, for example, in excess of 35 miles per hour.

Accordingly, a need exists for an integrated sensor system which willenable display of speed, water depth and water temperature over a widerange of parameters and especially at speeds in excess of about 35 milesper hour.

Lastly, it is important that the sensed signals of speed, temperatureand depth should be adequately isolated from each other to preventinterference between signals and resultant display error. This isespecially relevant in the case of interference between the relativelysmall echo return signals received from sonic transducer signalling. Inan integrated assembly which includes all three sensors, it is difficultto suppress such interference.

DISCLOSURE OF THE INVENTION

In the apparatus of the present invention, a sensor housing is providedfor enclosing (1) a sonic transducer assembly, (2) a temperature sensorcomprising, for example, a thermistor, and (3) a solid stateelectromagnetic sensor comprising a Hall-effect device. The housingconsists of a top end wall and four side walls, one of which isangularly inclined from top to bottom at an angle of about 20 degrees toconform to the inclination of the transoms of some vessels and enablemounting the housing on such transoms. Support members comprising planarstruts are fixedly attached to a side wall opposite the inclined wall.An impeller, or paddlewheel, is rotatably supported from the struts suchthat only the portion of the paddles below the struts is immersed in thewater in operation when the housing is suitably mounted on the transomand the marine vessel is at planing speeds. Thus, the paddlewheelsmerely pierce the water and are not required to move water around acavity, as in hull mounted enclosed paddlewheel speed sensors. For thisreason, cavitation does not occur at higher speeds. Furthermore, thepaddles are asymmetric in shape, in that the "leading" or front surfaceof the paddles is inclined at a different angle of inclination than the"trailing" or back surface of the paddles to maximize the difference incoefficients of drag between back and front surfaces, thereby avoidingstalling at low speeds. The large difference between fore and aftimpeller coefficients of drag not only eliminate impeller stall, butyields almost linear pulse output at low speeds.

The paddlewheel or impeller is formed of amorphous magnetic material andthe blades are magnetized to provide alternate North-South poles. As themarine vessel moves through water, the paddlewheel rotates at a rateproportional to the velocity of the vessel. A Hall-effect device mountedinside the housing adjacent the support members senses the change inelectromagnetic field as the polarized paddlewheels pass by andgenerates a square wave signal of 5-14 volts D.C. in amplitude; thefrequency of which is proportional to vessel speed.

The sonic transducer is centrally located inside the housing and isprovided with a metallic coaxial shield enclosure between it and theHall-effect speed sensing device to prevent reciprocal interferencebetween the signals generated by the Hall-effect device and the sonictransducer. The metallic shield is also interposed between the sonictransducer and the wall mounted temperature sensor, thereby similarlyreducing mutual interference between the two devices. Electrical leadsrunning from the sonic transducer, Hall-effect device, and thermalsensor are coupled to appropriate amplifiers and display devices on thevessel over a shielded cable through an opening in the end wall of thesensor housing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view partially cut-away of a three sensorassembly of the invention.

FIG. 2 is a partial block diagram, partial section along line A--A ofFIG. 1 showing the details of the interior of housing 40 and theelectrical connections from the sensors to the displays.

BEST MODE OF CARRYING OUT THE INVENTION

Referring to FIGS. 1 and 2, a speed or knot sensor is shown generally at10 to comprise a rotatable paddlewheel or impeller, rotatably mounted onshaft 17 supported between struts 11A and 11B, which are affixed to sidewall 40A of sensor housing 40.

The speed sensor also includes an electromagnetic sensing device 18which preferably operates on the Hall-effect principle. Sensor 18 ismounted on the interior side of wall 40A within housing 40 and laterallyadjacent between brackets 11A and 11B.

The paddlewheel 16 consists of a hub portion 16' from which extend sixpaddles 19. The paddlewheel is formed of amorphous magnetic material,such as barium ferrite by an injection molding process. After formationof the paddlewheel 16, the paddles may be electromagnetically polarizedin a magnetic field such that the polarity of the six paddles at the tipalternates from North to South, as shown in FIG. 2. Alternatively, thehub may be of one polarity and each of the paddles of an oppositepolarity. Other possible polarity patterns are contemplated depending onthe sensor application. In any event, as the paddles rotate about theshaft, the variation in electromagnetic field caused by the polaritychanges is sensed by the Hall-effect device 18 mounted on the interiorof side wall 40A adjacent to the paddlewheel.

The front and back surfaces 16a and 16b, respectively, of the sixpaddles, or impeller blades, 19 are angularly offset from each other toform an asymmetric shape which maximizes the difference in coefficientof drag between the front and back surfaces. Thus, as may be seen inFIG. 2, front surface 16a extends almost radially from the hub andconsequently has a relatively high coefficient of drag, whereas backsurface 16b extends tangentially from the hub and has a lessercoefficient of drag as it passes through the water. With this paddleconfiguration, the tendency to stall at lower speeds is greatly reduced.

The housing 40 is made of an electromagnetically permeable material,such as polycarbonate. Housing 40 consists of a plastic enclosure formedof a top end wall and four side walls, respectively 40C, 40A, 40B, 40Dand 40E. Side wall 40B is inclined at an angle of about 20 degrees fromtop to bottom, so as to enable convenient mounting of the sensor housingonto the transom of a marine vessel, some of which have similarlyinclined transoms. Members 60 and 62 are affixed to side walls 40E and40D, respectively. These members are provided with apertures 64 and 66to which mounting brackets (not shown) may be secured for mounting thehousing onto the transom.

A sonic transducer assembly 14 is centrally mounted within housing 40.Sonic transducer assembly 14 comprises a copper, or other electricallyconductive material, forming an electromagnetic shielding cup orenclosure 20 about a piezoelectric transducer, shown generally at 22.Piezoelectric transducer 22 consists of a piezoelectric element 2 and aresilient backing member 4, preferably consisting of cork material orequivalent. Cork material 4 encloses piezoelectric element 2 at the topand sides of the generally circular piezoelectric crystal 2. Electricalleads 38 and 36 are provided in electrical contact with the bottom andtop, respectively, of piezoelectric element 2.

A thermal sensing device, such as a well-known thermistor 12, is mountedon side wall 40D of housing 40, as shown in FIGS. 1 and 2. Electricalleads 34 and 32 are attached to the output of thermal sensor 12.Similarly, electric leads 30, 26 and 28 are attached to Hall-effectdevice 18, as shown more particularly in FIG. 2. All of these leads arecoupled out of the top of housing 40 through an opening provided in topwall 40C in a cable 21 which runs through grommet 25. Thus, as shown inFIG. 2, cable 21 includes six electrical leads which provide the inputand output signals to knot meter display 70, temperature display 80 anddepth indicator 90.

The ground connections for the device depend upon whether a balanced orunbalanced line is connected to the piezoelectric element 2. In theconfiguration shown in FIG. 2, an unbalanced line connection is shown toinclude a coaxial cable consisting of inner conductor 36 and outersleeve conductor 38. Conductor 38 is the shield or ground lead and it iscoupled to copper shield 20 by portion 38a of shield lead 38. Conductor36 is the signal lead and it is connected to the top surface ofpiezoelectric element 2. Center lead 28 from Hall-effect device 18 isalso coupled to ground by being coupled to shield 20, either directly or(as shown) by being attached to ground shield wire 38a. The combinationof the grounded shield, and the copper shield enclosure 20, providesinterference free coupling of signals from the interior of housing 40 tothe three display devices, 70, 80 and 90, mounted on the marine vessel.

In an unbalanced line configuration, the bottom face of element 2 isgrounded via shielded wire portion 38b, as shown in FIG. 2. In abalanced line, lead 38b is deleted and the front/bottom face of element2 is electrically "floating" or not grounded. B+ voltage is suppliedfrom a power supply (not shown) in display 70 via lead 30 to device 18.The speed output signal is fed from device 18 via lead 26 to the signalinput terminal of display 70.

The temperature circuit through thermistor 12 is completed from lead 32at display 80 through the thermistor and back to the display 80 via lead34. Similarly, the depth signal lead 36 at the top face of element 2 isfed to the signal input terminal of indicator 90 and the grounded shield36 of the coaxial cable is grounded at indicator 90.

The entire inner portion of housing 40 is encapsulated in pottingmaterial, such as polyurethane to insure water-tight encapsulation andat the same time, provide a path for sonic energy from piezoelectricelement 2 to travel unimpeded out the bottom of housing 40.Piezoelectric element 2 may comprise well-known lead zirconate titanatematerial, or barium titanate or other equivalent material.

The purpose of the cork material 22 enclosing the top and side walls ofpiezoelectric element 2, is to provide a barrier against unwantedtransmission of sonic waves toward the top of enclosure 40, rather thanin the preferred direction, out the bottom.

In operation, the paddlewheel impeller of speed sensor 10 is adapted tomount on the transom of a vessel in a position such that the paddles 19pierce the surface of the water when the vessel is planing. Also, thepaddlewheel is open at the rear, top and bottom. Therefore, the impellerblades or paddles are not attempting to move water around an enclosedcavity. This greatly improves the linearity of the speed sensor,especially at speeds in excess of 35 miles/hr. since cavitation wouldnormally occur at these high speeds in an enclosed paddlewheelconstruction.

As the paddlewheels rotate past Hall-effect device 18, a DC alternatingsquarewave voltage signal of an amplitude approximately equal to the DCinput voltage, i.e., typically 5-18 volts DC, is generated. Thefrequency of the voltage signal is directly proportional to therotational speed of the paddlewheel and therefore to the velocity of thevessel. As previously mentioned, a DC signal, labelled B+ in FIG. 2, isprovided from a power supply (not shown) over lead 30 through cable 21to Hall-effect device 18. The system will operate at an DC voltagebetween 5-18 volts. The output signal from Hall-effect device 18 iscoupled via lead 28 through cable 21 to the input signaI terminal ofknot meter display 70. The remaining lead 26 from Hall-effect device isgrounded to copper shield 20 and to housing 40.

Equivalents

This completes the description of the invention. It should be understoodthat the invention is not to be limited to the specific embodiment setforth herein, but only by the scope of the following claims, which willbe provided with the full range of equivalency to which such claims areentitled.

For example, it may be desirable to utilize only the speed sensor insome applications. In other applications, the speed sensor and depthindicator may be utilized instead of all three devices.

We claim:
 1. A marine transducer device adapted for mounting to theexterior transom of marine vessels comprising:(a) a housing in which anelectromagnetic sensor is mounted; (b) a pair of support membersattached to said housing and extending laterally therefrom adjacent saidelectromagnetic sensor; (c) a paddlewheel rotatably mounted in avertically unenclosed position between said support members forgenerating a patterned electromagnetic field which extends from thepaddlewheel to the sensor; (d) lead wires coupled to said sensor forcoupling pulsed electrical signals to display devices on said marinevessel said signals being linearly proportional to the rotational speedof said paddlewheel as said paddewheel rotates.
 2. The device of claim 1in which the electromagnetic sensor is a Hall-effect device and thesignal is a voltage pulse, the pulse rate of which varies in accordancewith the rotational speed of the paddlewheel.
 3. The device of claim 1,said paddlewheel comprising a wheel with a plurality of paddles on theperiphery of the wheel, said paddlewheel being vertically locatedbetween the support members in a position such that only a portion ofthe paddlewheel is immersed in water when the device is mounted on thevessel and the vessel is operated at planing speeds.
 4. The device ofclaim 1 in which the support members are struts extending from thehousing.
 5. A combination temperature sensor and speed sensor fortransom mounting on marine vessels as a unitary structure comprising:(a)a sensor housing in which are housed:(i) a temperature sensor device,and (ii) an electromagnetic sensor means for generating pulsed electricsignals in response to changes in electromagnetic fields; (b)paddlewheel for generating a patterned electromagnetic field rotatablymounted on struts affixed to an external surface of said housinglaterally adjacent said electromagnetic sensor and verticallyunenclosed, the paddles of said paddlewheel being disposed to partiallyextend into water when said sensor housing is mounted on said vessel. 6.A sensor device for external mounting on the transom of marine vesselscomprising:(a) a sensor housing adapted to be mounted on said transomand in which is mounted an electro-magnetic sensor; (b) strutsexternally attached to said housing adjacent said electromagneticsensor; (c) a paddlewheel rotatably mounted between said struts andvertically unenclosed for generating an electromagnetic field extendingto said electromagnetic sensor; (d) lead wires coupled to said sensorfor coupling electrical signals generated by said sensor to displaydevices on said marine vessel.
 7. The device of claim 6 including atemperature sensor mounted in said housing with lead wires coupled to adisplay device on said vessel.
 8. A sensor device for marine vesselscomprising:(a) a housing in which are mounted a temperature sensor andan electromagnetic sensor; (b) support members externally attached tosaid housing adjacent said electromagnetic sensor; (c) a paddlewheelrotatably mounted on said members and exposed on all sides except forsides adjacent said members and wherein in operation said paddlewheel isadapted to be partially submerged in the water when said vessel isplaning, the paddles of said paddlewheel generate electromagneticsignals proportional to the planing speed which are sensed by saidelectromagnetic sensor and converted to voltage pulses; (d) lead wirescoupled to said sensors and extending through wall of said housing forcoupling electrical signals from said sensors to display devices on saidmarine vessel.